Arc apparatus



April 22, 1941. H. G. SPEAR ARC APPARATUS Filed Jan. 13, 1940 4 Sheets-Sheet 1 INVENTOR. HOWARD G. Spa/4x2,

ATTORNEY.

April 22, 1941. H G. SPEAR 2,239,661

ARC APPARATUS Filed Jan. 13, 1940 4 Shuts-Sheet 3 I 138: I 176 I 186 INVENTOR. 156144420 G, 5.42,

BY W

ATTORNEY.

April 22, 1941. I H sPEAR 2,239,661

ARC APPARATUS Filed Jan. 13, 1940 4 Sho0ts-5heet 4 zil s INVENTOR.

HOWARD 6. J EAR,

Patented Apr. 22, 1941' ARC APPARATUS Howard G. Spear, North Hollywood, Calif., as-

signor, by direct and mesne assignments, to William E. Beatty, Los Angeles, Calif.

Application January 13, 1940, Serial No. 313,729

17 Claims.

My invention relates to electric arc apparatus wherein two carbon electrodes are fed to the arc by means of negative and positive heads.

While a motor common to both heads has been employed heretofore for operating the heads to feed the carbons, the motor drive has been I rather complicated. One object of the invention is to simplify the motor drive for the heads.

Also, it has been found that th terrific heat generated by the are results in damage to the heads. Another object of the invention is to reduce such damage.

A further object is to facilitate manual feed of the electrodes.

Another object is to independently adjust the rate of automatic feed of each electrode.

For further details of the invention reference may be made to the drawings wherein:

Fig. 1 is a front elevation of electric arc apparatus according to the invention.

Fig. 2 is a plan view looking upward at the bottom of the apparatus of Fig. 1.

Fig. 3 is a section on line-33 of Fig. 1. In this figure and others the sectional view is in the direction of the arrows.

Fig. 4 is an enlarged partial sectional view of the slip clutch shown at the left of Fig. 2.

like M (Fig. 5). Motor t carries and is coupled to a reduction gear l5 having a ratio of 60 to 1 and having a slow speed driven shaft l0. For example, if motor I runs'at 1725 R. P. M., shaft I 6 will run at about 28 R. P. M. Referring to Fig. the end bell 4' of the motor 4 is provided with a recess 203 in which the reduction gearing I5 is housed. Centrally of the end bell 4' and at the bottom of recess 203 is a circular recess 204 which serves as a bearing for the end of the motor shaft not shown. This motor shaft Fig. 5- is a sectional view on line 5-5 of Fig. 1.

Fig. 6 is an enlarged vertical sectional view of the positive head of Fig. 1.

Figs. 7, 8, and 9 are sectional views on lines -'l; -8 8; 9-3 respectively of Fig. 6.

ii ig. 10 is a plan view of the scroll gear of Fig. 6. Fig. 11 is a partial sectional view on line II-l I of Fig. 1.

Fig. 12 is a section on line |2 |2 of Fig. 11. fig. 13 is a section on line |3--l3 of Fig. 1. g. 14 is a section on line |4-|4 of Fig. 6.

Fig. 15 is a rear elevational view of the reduction gearing.

Referring to the drawings, the are light of Fig. 1 may be mounted in a suitable casing having a reflector not shown, and comprises a positive head I and a negative head 2 mounted on a base 3 and operated by a motor 4 mounted beneath base 3. Head is carried by a pedestal 5 which is secured to base 3 by bolts like I and insulated from base 3 by insulation 6. Head'l is secured to the top of pedestal 5 by bolts like 0 and insulated from pedestal 5 by insulation 3. Head 2 is mounted on pedestal 10 which is secured to the top of base 3 by bolts like II and insulated from base 3 by insulation l2.

' The base I3 of motor 4 bears against the underside of base 3 and is secured thereto by bolts carries a worm gear not shown which meshes with the worm gear 205 which drives the worm 206. Below worm 206 is a worm gear 201, the hub of which can be seen extending above worm 206. Worm gear 201 is mounted on the shaft IS. "The motor shaft not shown thus drives the shaft I8 through the reduction gearing comprising a worm not shown on the motor shaft, worm gear 205, worm 203 and worm gear 201. Rotatably mounted in base 3 directly above driven shaft I6 is the positive electrode drive shaft l1. Shafts I5 and I! are coupled or uncoupled by the slidable coupling l8. The lower end of coupling I0 is rotatably fixed to shaft [8 by the pin and slot I! while the upper end of coupling l0 may be moved into or out of rotating engagement with shaft H by means of the pin and slot 20. Coupling I8 is slid up or down by lever 2| having a forked end 22 which lies in a groove 23 in coupling l8. Lever 2| is pivoted at 24 to flange 25 depending from base 3. Lever 2| is held against depending flange 26 by spring 21. The top of lever 2| carries a cam 28 adapted to be engaged by shoulder 23 on shaft 30 which is slidably and rotatably mounted in flanges 25 and 26. The positive electrode drive shaft ll carries a gear 3| engageable with gear 32 on shaft 30 when the latter is moved to the left by handle'33, this movement causingshoulder' 29 acting on cam 28 to depress lever 2| and uncouple shafts l6 and I1 whereby shaft I1 is disconnected from motor 4 and connected to shaft 30 to feed the positive electrode by hand.

Slow speed driven shaft I6 serves also to drive the negative head and for this purpose coupling l8 carries an eccentric 34 adapted at times in its rotation to engage follower 35 on lever 36 (Fig. 2), to oscillate that lever and actuate slip clutch or one-way clutch 31 to rotate th negative electrode drive shaft 38 (Fig. 3) step by step. Follower 35 is shown as a disk rotatably secured to one end of lever 30 by a bolt 39.

Adjacent follower 35 and mounted on one end of lever 36 is an adjustable stop screw 40 which limits the movement of follower 35 towards eccentric 34 by engaging the casing of the reduction gearing I as shown in Figs. 2 and 5. Lever 33 is pivoted intermediate its ends at 4| to a flange 42 depending from the base 3 which carries a stud 43 which serves as a pivot and stud 43 has a leaf spring 44 which engages projections 45 and 43 at opposite sides of the pivot 4| to urge the lever 33 in a clockwise direction so that stop 43 will engage the casing of gearing I5 at times when eccentric 34 is out of engagement with follower 35.

The other end of lever 33 is provided with a projection 41 adapted to engage the lever arm 43 which is rotatably mounted in a bearing 43a (Fig. 3) in the horizontal extension of the flange 53 depending from the underside of base 3. When projection 41 moves downwardly it rotates the lever arm 43 clockwise as seen in Figs. 2 and 4, and when projection 41 movesup, the lever arm 43 is rotated in a counter-clockwise direction by reason of the spring 43 connected between the lever arm 43 and the left end of lever 33. One side of lever arm 43 is provided with a tapered bore 5| in which is mounted a ball 5|a which rides partly in a race way 52 in disk 53. Ball 5|a is urged towards the narrow part of bore 5| by means of spring 54, the tension of which can be adjusted by screw 55 mounted at one side of the lever arm 43. When arm 43 is rotated clockwise, as seen in Fig. 4, ball 5Ia is wedged in the narrow part of bore 5| and serves to couple lever arm 43 to disk 53 to rotate them together. When lever arm 43 is rotated counter-clockwise as seen in Fig. 4, ball 5|a moves into the larger part of bore 5| so that disk 33 is not rotated thereby. The throw of lever 35, acting through slip clutch 31 thus determines the amount that the negative electrode 33 is fed forward each time, and the stop screw 43 makes it possible to adjust the 3 amount of this feed to a very fine degree. Rotation of disk 53 is frictionally retarded by spring pressed brak 53 having a shoe 51 engaging groove 52. Disk 53 carries one or more pins 53 adapted to be embraced by slots 53 in the flange 33 on sleeve 3| which is rotatably mounted in the bore of lever arm 43, as shown in Figs. 3 and 4.

Lever arm 43, as shown in Fig. 3, has a vertical sleeve 32 surrounding sleeve 5|. Sleeve 32 has its upper end threaded and provided with a nut 33, this nut resting on the top of the horizontal bearing portion of flange 53, and the top of lever arm 43 engages the under portion of this horizontal flange whereby the arm 43 is restrained from vertical movement. Also disk 53 is restrained from vertical movement by reason of the fact that the top of it lies against the underside of lever arm 43, and its underside lies aibove overhanging flange 34 on arm 43, as shown in Fig. 2. The sleeve 5| however is slidable in sleeve 32 and disk 53 and when moved downwardly sleeve 3| is uncoupled from the negative electrode driveshaft 33 at the pin and slot 23 and also sleeve 3| is uncoupled from disk 53 since the notches 53 will extend below and not engage pins 53. The purpose of thus disconnecting shaft 33 from the slip clutch 31 is to disconnect shaft 33 from motor 4 and permit shaft 33 to be operated by the handle 13 so that the negative electrode may be fed by hand. Shaft 33 at its lower end carries a collar 1| having a groove 12 in which rides the forked end 13 of lever 14 pivoted at 15 to flange 15 which depends from the base 3. Depending from base 3 is another flange 11 and the shaft 13 upon which handle 13 is mounted is slidably and rotatably mounted in flanges 13 and 11. Shaft 13 carries gear 13 adapted to be engaged with gear 33 on shaft 33. When shaft 13 is moved to the right, shaft I3 is urged to the left by a spring 3| between one side of flange I5 and the cam 32 which is fixed on shaft/13. Lever 14 has a projecting end 33 adapted to rest on and be actuated by cam 32. When shaft 13 is moved to the right, the end 33 of lever 14 rides down the surface of cam 32 under action of spring '34 so that lever 13 moves in a clockwise direction to uncouple shaft 33 from motor 4 as above described. When shaft 13 is moved manually or by spring 3| to the left, shaft 33 is coupled to motor 4.

The handle 13 may also be used to advance the negative electrode 33 to strike-the are as follows; cam 32 is provided on its front face with a series of teeth 35 having flat faces extending longitudinally of cam 32 as shown. A corresponding set of teeth 33 are formed on lever 31 which loosely fits on shaft 13. Lever 31 is pivotally connected at 33 to rod 33 (Fig. l) which is normally pulled upwards by spring 33 connected to rod 33 and to the pedestal I3. At its top, rod 33 is pivotally connected at 3| to a lever 32 (Figs. 1 and 12) fixed to a rotatable pinion 33, meshing with rack 34 on the carriage 35 of the negative electrode 33. When the handle 13, as shown in Fig. 2, is rotated counter-clockwise, the teeth slide over teeth 35 without rotating lever 31 about shaft 13. When handle 13 is pulled out as shown and is rotated clockwise, the fiat faces of teeth 35 and 33 engage to cause lever 31 to move about shaft 13 as a pivot, whereby lever 31 is moved downwards as seen in Fig. 1, and the negative electrode 33 is moved to contact the positive electrode 33 whereupon the release of handle 13 will permit spring 93 to rotate pinion 33' counter-clockwise and separate the electrodes to strike the arc.

Carriage 35 has pivotally mounted thereon two levers 31 and 33 carrying at their front ends feed wheels 39 and I33 respectively, as shown in Figs. 11 and I2, and the latter are operated by pinions I3I and I32 (Fig. l), the latter meshing with worm I33, as is well known. Worm I33 is connected through a flexible coupling I34 to shaft I35 which has a slidable coupling I33 and flexible coupling I31 with shaft 33" connected through removable insulating coupling 33' (like coupling I59) with shaft 33 (Fig. 3).

Projecting from the front of carriage 35, as shown in Fig. 11, is an arm I33 terminating in a two piece ring I39 which engages a circular groove H3 in the terminal block III. The two parts of the ring I33 are held together by screws H2 and H3, as shown in Figs. 1 and 11. Arm I33 is slightly wider than the distance between the centers of pinions I32 and IN, as shown in Fig. 1. Terminal block III has an aperture II2 toreceive the carbon 33 and in alignment therewith is an apertureII3' in a disk II4 of carborundum carried by a ring II5, supported by outwardly extended arms 3 projecting from the end of terminal block III. The latter has one 'or more radiating flanges II1, as shown. Terminal block III is electrically connected to arm I33 by conductor II3, fastened to block III by screw I23 and to arm I33 by screw |2I which also makes contact with the top end of flexible conductor I22 (Fig. 1) arising from bus bar I23 which is insulatingly mounted in base 3 and Secured thereto by nut I24, companion nut I25 serving to retain the lug not shown of one side of a power line. The provision of extended arm I08 with terminal block III thereon having flanges Ill and with an air space between terminal block III and the insulating material II4 all contribute to insulate the feed wheels 99 and I and associated parts from the heat of the arc.'

As shown in Figs. 1 and 13, the terminal block III is provided with the following means to resiliently hold the electrode 69 in electrical contact with terminal block III. Underneath terminal block III there is provided an aperture in which is slidably mounted a shoe I21 having a pin I28 riding in groove I29 t: prevent rotation of the shoe. Secured underneath terminal block I. by means of bolts I30 is an arcuate flange I3I which has secured thereto as by soldering, a metal tube I32 carrying a series of balls I33, the upper one of which bears against shoe I21 and against the lower one of which bears a spring I34 as shown in Fig. 1 Mounted in the end of tube I32 is an adjusting screw I35 to vary the pressure on spring I34 and vary the pressure of shoe'I21 on electrode 69. If it is convenient to have tube I32 project straight from terminal block III as later described in connection with the positive head, the spring follower may take the form of a rod instead of a series of balls I33. By providing a spring follower, it is possible to have the spring. I34 positioned a substantial distance away from the electrode 69.

thereby preventing the heat of that electrode from removing the temper from the spring.

The feed mechanism for the positive head is substantially the same as that shown in the U. S. patent to Anderson 2,173,149 issued September 19, 1939. Some differences comprise an improved form of terminal block and the provision of an electrode release.

To protect the positive head from the heat of the are, as shown in Figs, 1 and 6, I support a disk I36 wof insulating material at the front of the positive head I, by means of screws like I31. Secured to the front of disk I36, is terminal block I38 secured thereto by screws like I39 in Fig. 6. Terminal block I38 has radiating flanges I38a and it terminates in a ring I40 carrying a disk of carborundum I4I. Between ring I40 and the body portion of terminal block I38, as shown in Fig. 14, is a circular array of holes H011 to facilitate radiation of heat from the carborundum disk I. I36 and MI, of course, have central alignedapertures for the positive electrode 96. The contact shoe for terminal block I38 is similar to that provided for the negative electrode except that a follower I42, in the form of a rod, is used instead of a series of balls. Rod I42 bears against contact shoe I43, as shown in Figs. 6 and 14 in order to urge the electrode 96 against the terminal block I38, acting under control of spring I44 the tension of which may be adjusted by screw I45. Rod I42, spring I44, and screw I45 are mounted in tube I46 soldered to arcuate .block I41 which is secured to the underside of terminal block I38 by bolts I48 and I49. Shoe I43 rides in aperture I50 in terminal block I38 and it has a pin I 5| riding in a groove I52 to prevent its rotation.

Electric current is fed to the positive electrode 96 by flexible conductor I53 which is secured to ring I40 by screw I54. The lower end of flexible.

conductor I53 is connected at I 55 to the top of a bus bar I56 suitably insulated from and secured to the base 3 as generally represented .at I51. One side of the power line is connected to the bus bar I56 by means of nut I58.

The positive electrode drive shaft Ilhas fixed The terminal block I38 and the disks thereto a. sleeve I59 carrying a pin I=60 embraced by the forked end I 6| of shaft I62 in order to provide a slip coupling to permit the casing I63 to be removed. Shaft I62 has a universal joint I64 connected with the stubishaf-t I65 on which a pinion I66 in Fig. 6 is mounted. Casing I63 is secured to casing I64 of the positive head I, by means of bolts I64a as shown in Fig. 7. The bolts 8 shown in Fig, 1 hold the casing I64 to pedestal 5 so that the latter may be left in position on pedestal 5 and casing I63 removed from casing I64 by removing bolts I64a, as described in the above mentioned patent. Pinion I66 meshes with gear I61 fixed to tubular member I68 by means of the clamping action of nut I69 as described in the above patent. Gear I61 carries a cam I10 having a cam follower III which, at certain times, allows adjusting screw I12 to engage the teeth I13 of a scroll gear I14 toarrest the rotation of the same and cause the feed wheels I 15 and I16 to rotate in a planetary manner about their own axes to propel forward the carbon 96 as described in the above patent. According to the present invention, provision is made for the release of the feed wheels I15 and I16 as follows; inside of tubular member I68 is mounted a sleeve I11 carrying an enlarged head I18 against which the lever I19 is adapted to bear so that when lever I19 which is pivoted to casing I63 at I80,

against the electrode 96.

is moved to the left by handle I8I, the sleeve I11 which is slidably mounted in tube I68, will be moved to the left to push the feed wheels I15 and I16 away from the electrode 96, or away from the bore of sleeve I11 so that an electrode may be inserted in the positive head without injury due to gouging by the feed wheels I15 and I16. Sleeve I68 carries an operating head I82 which terminates substantially within the periphery of the feed wheels I15 and I16, as shown in the dotted lines in Fig. 6.' Operating head I82, as in the above patent, has cross slots I83 and I84 for the feed wheel shafts I85 and I86 respectively, as well as longitudinal slots I81 and I88, which house the feed wheels I15 and I16 so that they may bear In line with the slots I81 and I88, I provide slots I89 and I90 in the operating head I9I on sleeve I11. As shown in Fig. 9 and also in Fig. 6 in dotted lines, the head I9I at opposite sides, carries pins or stub shafts I92 and I93 on which are pivotally mounted and therefore self-centering, wedge plates I94 and I95 respectively. One of these plates I95 is shown in dotted lines in Fig. 6. The wedge plates I94 and I95 are prevented from sliding off from their respective pins I92 and I93 by the springs 200 and 20I respectively. As shown in Fig. 8, the wedge plates I94 and I95 are flat and bear against the opposite outside flat faces of the head I82. Also wedge plates I94 and I95, as shown in Fig. 8, extend between the shafts I85 and I86 and have such a width that when they are urged to the left, the shafts I85 and I86 ride on the surfaces of those wedge plates, the shafts I85 and I86 moving outwardly in their respective slots Hi3 and I84, against the action of'springs 200 and 20I until the feed rollers I15 and I16 are separated sufficiently to clear the electrode 96. When handle I8I is released, the tension of springs 200 and 20I acting in conjunction with the slope of the wedge surfaces of the wedge plates I94 and I95 is sufficient to move those wedge plates and tube I11 to the right until the feed rollers I15 and I16 contact the electrode 96, or until the their respective slots I83 and I84.

It will be understood that by varying the setting of the stop screw 40, in Figs. 2 and 5, the extent of movement and therefore the speed of the step-by-step movement of the negative electrode drive shaft 38 will be correspondingly varied. Independently thereof the speed of the positive head I may be varied by adjusting the screw I12. The speed of the positive head I and the negative head 2 may therefore be varied independently of each other while the motor 4 is running at a constant speed.

I claim:

1. Are apparatus comprising a metallic housing having a bore to receive the electrode, said housing having an aperture opening into one side of said bore, a pressure shoe in said aperture, a tubular casing, means for securing said casing to said housing, a spring in said casing removed from said shoe, a follower in said casing between said spring and said shoe, and meansfor varying the tension of said spring.

2. Arc apparatus according to claim 1, wherein said tubular casing is curved away from the arc end of said housing, said follower comprising a series of balls.

3. Are apparatus comprising an electrode feed casing having a disk ofheat insulation, an electrode holder carried by said disk, a pressure shoe in said holder, and a disk of heat insulation carried by said holder in front thereof, said disks and said holder having aligned electrode apertures.

4. Arc apparatus comprising the combination of a base, positive andnegative electrode drive shafts spaced apart, a motor on said base between said shafts, a reduction gearing carried by one end of said motor and having a vertical driven shaft, means coupled to said driven shaft for continuously driving said positive electrode drive shaft, and means actuated by said driven shaft for driving said negative electrode drive shaft step by step.

5. Are apparatus comprising the combination of a base, a constant speed positive electrode drive shaft, 9. motor on said base, a reduction gearing carried by said motor and having a vertically extending driven shaft directly coupled to said first mentioned shaft, a negative electrode drive shaft, and slip clutch means operated by said driven shaft for coupling said driven shaft to said negative electrode drive shaft.

6. Arc apparatus comprising the combination of a base, a positive electrode drive shaft extending through said base and rotatably mounted therein, a motor beneath said base, a reduction gearing coupled to said motor and having a vertical driven shaft in alignment with said positive electrode drive shaft, a clutch between said last two mentioned shafts, a gear on said positive electrode drive shaft, a stub shaft mounted beneath said base for bodily movement and having a negative electrode drive shaft extending I through said base and rotatably mounted therein adjacent the other end of said motor, and means actuated by said driven shaft for rotating said negative electrode drive shaft step by step.

8. Are apparatus comprising the combination of a base, a motor beneath said base, a reduction gearing coupled'to said motor and having a vertically extending driven shaft at one end of said motor, an electrode drive shaft extending through said base at the other end of said motor, and means operatively coupling said driven shaft and said drive shaft.

9. Are apparatus comprising the combination of a base, a motor beneath said base, a reduction gearing coupled to said motor and having a vertically extending driven shaft, an electrode shaft extending through said base in line with said driven shaft at one end of said motor, a coupling between said electrode shaft and said driven shaft, a second electrode through said base at the other end of said motor, means operatively connecting said second electrode shaftand said driven shaft, and means comprising handles at the front of said base for operating each of said electrode shafts for disconnecting its respective electrode shaft from said motor and for manually rotating its respective electrode shaft.

10. Arc apparatus comprising the combination of a base, a motor under said base, a reduction gearing coupled to said motor and having a vertical driven shaft, a positive electrode drive shaft carried by said base in line with said driven shaft at one end of said motor, means for coupling said shafts, an eccentric on said driven shaft, a negative electrode shaft carried by said base at the other end of said motor, a rocker pivoted intermediate its ends; a follower on one end of said rocker for said eccentric, stepping mechanism connecting the other end of said rocker and said negative electrode drive shaft, and an adjustable stop associated with said follower for varying the speed of said negative electrode drive shaft.

11. Arc apparatus comprising the combination of a base, spaced negative and positive drive shafts extending substantially parallel through said base, a motor between said shafts, means associated with each of said shafts for coupling the same to said motor, and means comprising a hand operating device at each end of said motor for operating said coupling means respectively and for manual rotation of said negative and positive drive shafts respectively.

12. Are apparatus comprising the combination of a base, a motor on said base, a negative electrode drive shaft on said base, a clutch between said motor and said shaft, a gear on said shaft, a stub shaft on said base having a handle, a gear on said stub shaft, a striker arm, means associated with said stub shaft for operating said striker arm, and means associated with said stub shaft for engagement and disengagement of said gears and for operating said clutch.

13. Arc apparatus comprising the combination of a motor, a reduction gearing therefor, a constant speed drive shaft coupled to said gearing, a positive head coupled to said shaft, means associated with said head for adjustably feeding a positive electrode step by step, a step by step rotatable negative electrode drive shaft, a negative head therefor, and a slip clutch associated with said gearing and said negative electrode drive shaft for adiustably driving said negative head step by step. i

14. Arc apparatus comprising the combination shaft extending of a base, a motor on said base, a reduction gearing coupled to said motor and having a vertical driven shaft, a positive electrode drive shaft coupled to said driven shaft, an eccentric on said driven shaft, a negative electrode shaft at the other end of said motor, a rocker pivoted intermediate its ends, a follower on one end of said rocker for said eccentric, stepping mechanism connecting the other end of said rocker and said negative electrode drive shaft, and an adjustable stop associated with said follower for varying the speed of said negative electrode drive shaft.

15. Arc apparatus comprising the combination of a slidable negative head,asupport therefor, a step by step rotatable negative electrode drive shaft coupled to said head for feeding the negative electrode, a motor having a slow speed shaft substantially parallel to and spaced from said drive shaft, a slip clutch operatively connecting said slow speed shaft and said negative H electrode shaft, and means for adjusting the angular throw of said clutch to vary the negative feed.

16. Are apparatus comprising the combination of a. motor having a slow speed shaft, an eccentrio on said shaft, a slip clutch operated by said eccentric, means for varying the throw of said clutch, a negative electrode drive shaft operated by said clutch, a constant speed positive electrode drive shaft coupled to said slow speed shaft, a positive head operated by said positive electrode drive shaft for rotating and longitudinally feeding the positive electrode, and means associated with said positive head for varying the positive feed.

1'7. Arc apparatus comprising the combination of a positive head, a rotatable electrode carrier therein for advancing the positive electrode, a negative head, a step by step rotatable negative electrode drive shaft forsaid negative head, a motor, means coupling said motor to said rotatable carrier, one-way clutch means coupled to said motor for actuating said negative electrode drive shaft step by step, means for varying the amount the positive electrode is fed forward for each revolution of said positive electrode carrier, and means comprising an adjustable stop for said clutch for varying the extent of each step of said step by step movementof said negative electrode drive shaft.

HOWARD G. SPEAR. 

